TECHNOLOGY OVERVIEW

Variables Sampling Plan - Fraction Defectives - Standard Deviation Unknown

BIS.Net Team

Variables acceptance sampling plans are used when quality characteristics are measured on a continuous scale. Variables sampling plans tend to be more efficient than Attributes Sampling plans with a much lower sample size.

This type of sampling plan protects against the receipt, or release of lots with excessive defectives. Defectives are items where measurements fall outside specification limits. For example, moisture content may be specified for a delivery of a raw material. If the percentage of moisture that falls outside specification limits is excessive the lot will be rejected. The proportion falling outside specification limits is called fraction defective. The percentage is called percent defectives, which is 100 times the fraction defectives.

This plan is used if the standard deviation is unknown.

The unknown standard deviation plan requires for you to specify the lower and upper specification limits, the AQL and LTPD, including the producer’s and consumer’s risks. The sample standard deviation must be computed after the lot has been sampled. The sample standard deviation will be used in a calculation that must be performed after sampling to decide whether the batch must be rejected or is accepted.

The BIS.Net Acceptance Sampling Plan App provides an OC CURVE and the Sampling Plan for its output, such as shown below.